The equilibrative nucleoside transporters are integral membrane proteins that are essential for the uptake of nucleosides and chemotherapeutic nucleoside analogs (e.g. Ara-C, gemcitabine). Enhanced sensitivity to nucleoside analogs has been observed after combined chemotherapy (i.e. cisplatinum, irradiation), although the mechanism(s) responsible for these effects are poorly understood. The equilibrative nucleoside transporters (ENT1/2) are ubiquitously expressed and are differentially regulated depending on the exposure of cells to mitogens or stress signals. At present, the molecular events that control the transcriptional regulation of these transporters are unknown. Our lab has been investigating the regulation of pyrimidine nucleotide synthesis by protein kinases. Our recent studies have focused on the requirement of ENT 1/2 in the uptake of nucleoside and the salvage synthesis of pyrimidine nucleotides. Specifically our studies have pointed to a crucial role for Src and the stress-activated c-Jun kinases (JNK) in the regulation of ENT1/2 expression. Thus the objective of this proposal is to characterize the kinase-dependent signals that are necessary for the transcriptional regulation of ENT 1/2, and to determine the impact of this event on cell proliferation or survival. In addition, we will determine the promoter elements that are required for kinase-mediated regulation of ENT1/2 expression. Finally, we will investigate whether activation of JNK is involved in the up-regulation and enhanced sensitization of cells to nucleoside analogs. The Specific Aims of the proposal are: Aim #1. Determine the involvement of specific protein kinases in the regulation of ENT1/2 expression. Aim #2. Elucidate the promoter elements necessary for the expression of ENT1 and ENT2. Aim #3. Examine the specific roles of ENTs in growth, differentiation and chemosensitization .